docs: def train(self, sentences, model):
          """Train the CRF tagger using CRFSuite.
  
          :params sentences: Annotated sentences.
          :params model: Path to save pickled model.
          """
          trainer = pycrfsuite.Trainer(verbose=True)
          trainer.set_params(self.params)
          for sentence in sentences:
              tokens, labels = zip(*sentence)
              features = [self._get_features(tokens, i) for i in range(len(tokens))]
              trainer.append(features, labels)
          trainer.train(model)
          self.load(model)